1. Field of the Invention
This invention relates generally to a revolving cam-type press, and more particularly to a revolving cam-type press suited for forming a cold-extruded part, a blanked part, a drawn part and so on with a high degree of precision.
2. Description of the Related Art
Mechanical presses have heretofore been widely known. For example, Japanese Patent Unexamined Publication No. 60-210398 describes in FIGS. 1 and 5 a mechanical press in which a reciprocally-movable slider (17) is connected through a rod (15) to an outer peripheral portion of a fluctuating disk (13) movable about a drive shaft in a fluctuating manner.
A mechanism employing a revolving cam is known, for example, from U.S. Pat. No. 3,673,951. This mechanism is used in a fodder, and as seen from FIG. 6 of this U.S. patent, a fluctuating motion, caused by the rotation of the revolving cam (80), is converted into a rectilinear motion through a disk (88).
Japanese Patent Unexamined Publication No. 5309493 discloses a cam-type press on which the present invention is based.
This press comprises a revolving cam rotatable with a drive shaft, a fluctuating disk for fluctuating movement in accordance with the rotation of the revolving cam, and a plurality of fluctuating disk rotation-prevention pins provided on one side of the fluctuating disk facing opposite to the revolving cam to be parallel to the drive shaft, and arranged in a circle concentric with the drive shaft, each of these prevention pins having a spherical head. This construction is analogous to that of the present invention.
In the first-mentioned mechanical press making use of the fluctuating disk, since the fluctuating disk (13) is supported only by a movable shaft (6), a span between a point of force with respect to a working load during a pressing operation, and the movable shaft is large, and the rigidity of the fluctuating disk is low. As a result, it has been impossible to obtain a worked product of a high precision.
Moreover, a cross spider-type universal joint serves also as a rotation prevention pin mechanism for preventing the fluctuation disk from rotation with the drive shaft, and therefore this rotation prevention mechanism lacks sufficient rigidity and durability particularly for a large drive torque produced during a pressing operation.
Furthermore, since the universal joint itself is a non-uniform joint, a stable transmission of the rotation can not be obtained, and it creates a source of production of mechanical vibration and noises. Therefore, it can not be expected to provide a machine capable of producing products with a high working precision.
The latter mechanism is a revolving cam-type drive mechanism, and when an axial load is applied to the revolving cam upon rotation of the drive shaft, a radial load perpendicular to the drive shaft acts on the revolving cam. And besides, in an embodiment described in the above publication, any means for bearing an axial load is not provided at the back side of the revolving cam.
Therefore, when an axial load is exerted on the revolving cam, a large bending moment acts on the drive shaft. As a result, a large stress acts locally on portions of thrust-bearing balls interposed between the revolving cam and the disk, so that the lifetime of the balls is shortened, which results in damage to the machine.
Moreover, since the axis of fluctuating movement of the disk is offset from the axis of rotation of a universal joint, a bending moment developing at the drive shaft is large, and therefore a large rotation drive force is required, so that a stable fluctuating movement of the disk can not be expected. As a result, this mechanism fails to provide a stable revolving cam-type drive mechanism with high-precision, and therefore even if this mechanism is used, for example, in a pressing machine, such pressing machine will not be stable and high in precision.
In the press disclosed in the above-mentioned Japanese Patent Unexamined Publication No. 5-309493, the rotation prevention pins each having the spherical head prevent the fluctuating disk from rotation; however, a sliding portion of the rotation prevention pin is constituted by the pin itself, thus providing a heavy sliding movement, and also lateral stresses are applied to the rotation prevention pins during the fluctuating movement of the fluctuating disk, so that this mechanism exhibits a poor followability. And besides, it has been necessary to balance forces of compression springs provided above and below the pins so that the spherical heads of the pins can always be disposed in a concentric path about an axis of rotation. Therefore, high-precision component parts have been required, and hard to take charge of.